Now is all clear. I checked the transistors: both are OK. Lucky me !
2SA1020G comes in SOT-89 package also (is written in the datasheet). They might be obsolete but are more than enough for the application (driving the MOSFETs with under 20V when they have a Vds=50V). No point to replace them if they work.
I replaced all power MOSFETs (16) and some Zenner surge suppressors with higher voltage rating versions and some burned resistors and the DC converter works again. I thank everyone for helping me identify those transistors.
BTW: To who is curious, this is the DC-DC converter from HI Voltage to Battery Voltage from the MPI 5,5K Hybrid Inverter made by MPP Solar. Was partially my fault that it failed. I set a 61V battery charging voltage, not knowing the Zenner surge suppressors across the MOSFETs were rated to 60V max. A bug in the software and Blam ! :) Now I know.